I had never heard of this term and did a search. Here's what I came up with:

Erythema Nodosum:

A tender, red, nodular rash on the shins that usually arises in conjunction with other illnesses, such as streptococcal, fungal, or tubercular infection. Also may occur with inflammatory bowel disease, occult cancer, or sarcoidosis. Because it's usually associated with a serious disease, a diagnostic search for the underlying cause is normally done. Sometimes though, NO underlying cause is found.